1. Field of the Invention
This invention relates to a connecting method and a connecting structure of printed circuit boards.
2. Description of the Related Art
Conventionally, solder is used to connect terminals of a flexible printed circuit board and a rigid printed circuit board. For instance, “Guidance to High Density Flexible Board” (written by Kenji Numakura, printed by Nikkan Kogyo Co. Ltd.) discloses on page 100 a connecting structure of a rigid (hard) printed board and a flexible board due to thermal fusion of solder. According to this structure, as shown in FIG. 1, a land 60a of a rigid printed board 60 is connected with a land 61a of a flexible board 61 by solder 62. The flexible board 61 is adhered to the rigid printed board 60 by adhesive 63.
However, when connection of terminals (lands) of the two boards is achieved by using the solder 62 as shown in FIG. 1, if the amount of solder is excessive, solder bridges are occasionally formed between adjacent two lands. That is, when the lands, which are overlapped with each other after the solder is supplied, is heated and pressurized, the solder is fused to have flowability. At that time, despite very low wettability of an insulating substrate material to solder, if the amount of the solder is excessive, the pressurized solder can flow out from the land to the insulating substrate and to the neighboring land so as to form solder bridges.